In Tennessee, the Democratic mayor of Nashville, Freddie O’Connell, said that in recent days, a rainbow crosswalk painted in honor of the city’s L.G.B.T.Q. community had been defaced. White supremacists waving Nazi flags had made repeated appearances downtown. “My biggest fear,” he said, “is that social fabric, even at the local level, continues to deteriorate.”

In Wisconsin, Dan McNeil, 71, a Democratic school board member in the farming town of Barron, called the situation “scary.” “You walk into a place in town, and it is, like, ‘Whose side are you on? Are you a liberal Democrat or a Trumper?”

An hour away in St. Croix County, Scott Miller, 42, who said he is a member of the local Republican Party, wondered if it was already too late: “These corporations are putting out millions and trillions in profits, donating unlimited amounts to politicians,” he said. “How can the average person compete?”

In California, Frank Xu, 46, of San Diego, expressed deep disillusionment in the dysfunction he saw in the aftermath of Saturday’s shooting, a far cry from the political and civic wonderland he embraced when he moved to the United States in 2005 from China. Like many young Chinese in the 1980s and 1990s, he said, he had been conditioned to stay out of politics and to be suspicious of political officials and their motives. A Republican, he had organized against affirmative action in his state, wide-eyed at the difference one person could make in this country.

Then came the Jan. 6, 2021, insurrection, which left him wondering whether to leave his presidential ballot blank in November. He has leaned back toward voting for Mr. Trump since the shooting. But like many other naturalized citizens, he has been viscerally reminded of the instability and violence he sought to escape in the United States.